The present invention relates to an apparatus and a method for reproduction from a recording medium. More particularly, the invention relates to an apparatus and a method for reproduction from a recording medium comprising a plurality of data tracks and having data track numbers recorded in conjunction therewith.
There exist rewritable disc-shaped recording media allowing users to record music and other data thereon. Such recording media each comprise two kinds of areas, one storing data representing pieces of music and other items, the other being a control data area (called a user's table of contents (TOC), or simply the U-TOC hereinafter) used to control unrecorded (i.e., free) disc areas. The control data in the U-TOC is updated every time a recording, edit or erase operation has been carried out.
Illustratively, when a piece of music is to be recorded on such a disc-shaped recording medium by a recording apparatus, the apparatus searches for and finds a free area on the disc by resorting to the U-TOC. The audio data is then recorded to the free area thus found. When a piece of music is to be reproduced from the disc, a reproducing apparatus identifies the disc area holding the target piece of music (represented by a specific data track) in accordance with the U-TOC. The area so identified is accessed for data reproduction therefrom.
Such disc-shaped media as magneto-optical discs are much easier to access randomly than tape-shaped recording media such as DAT's (digital audio tapes) and compact cassette tapes. On the disc-shaped medium, there is no need for data to be recorded in an orderly manner from inner to outer tracks (i.e., from the first to the n-th track). That is, even if a plurality of pieces of music are recorded in physically discontinuous locations on the disc, these pieces of music will be reproduced in a desired order as long as their addresses are properly controlled.
Furthermore, a single data track need not necessarily be composed of contiguous segments (physically continuous portions storing data); the track can be constituted by a plurality of discrete segments scattered over the disc.
This feature is applied advantageously to systems that read data from a magneto-optical disc, place temporarily the data so read into a buffer memory at a high transfer rate, and read data from the buffer memory at a low transfer rate as audio reproduction signals to be demodulated. Access to the target data ranging from one discrete segment to another may sometimes lead to a temporary discontinuation of the data being read from the magneto-optical disc, but the reproduced audio signals will be output uninterrupted.
Access to each segment for recording or reproduction may be repeated by taking advantage of the time difference between the high-speed writing of data to the buffer memory and the low-speed reading of data therefrom. That is, a new segment can be accessed before the remaining accumulated data in the buffer memory is read therefrom and exhausted for recording or reproduction. The process of recording or reproducing, say, a piece of music is carried out uninterrupted even where that piece of music is divided into a plurality of physically discontinuous segments.
It is possible, as shown illustratively in FIG. 1, that the first and the second piece of music are recorded contiguously in segments M.sub.1 and M.sub.2 and that the fourth piece of music is divided and recorded in segments M.sub.4(1) through M.sub.4(4) and the fifth in segments M.sub.5(1) and M.sub.5(2). It should be noted that what is shown in FIG. 1 is merely a schematic view. In practice, one segment can often range from several to several hundred tracks or more.
Where pieces of music are to be recorded to or erased from the magneto-optical disc, free areas can occur conventionally on tracks due to the different playing times of these pieces of music. But the discrete recording as outlined above makes it possible optimally to utilize the free areas on the disc in recording, say, a piece of music in place of a longer one that has been erased. There no longer occur unrecorded data recording areas left unused as a result of repeated recording and erasing operations on the disc. The magneto-optical disc can store not only pieces of music but also any other audio signals. In this specification, however, it is assumed for the sake of description that one data track is to record one piece of music.
On such discs, each piece of music must be recorded continuously by accessing segments constituting a plurality of free areas; to reproduce a piece of music from the disc requires gaining access to the appropriate segments in the correct order. The data used to connect the segments composing one piece of music (e.g., M.sub.4(1) -M.sub.4(4)) and the data indicating free areas are retained in the U-TOC. As mentioned, the U-TOC data are updated every time a recording or erase operation is carried out on the disc. The recording/reproducing apparatus controls the recording or reproducing process in accordance with the U-TOC data read out for head access operations on the disc.
As depicted in FIG. 2, data is recorded on the disc in units of clusters CL each comprising a total of 36 sectors, 4 sectors making up a subdata area and 32 sectors constituting a main data area, each sector being composed of 2,352 bytes. One cluster, corresponding to a few tracks, is the unit in which to record data. Each sector is assigned its unique address. The four-sector subdata area is used not only as a subdata area but also as a linking area. TOC data, audio data and other data are recorded in the 32-sector main data area.
Each sector is divided into sound groups. Specifically, two sectors constitute 11 sound groups. One sound group has 512 sampled items of data recorded therein separately for the left and right channels. The data in one sound group amounts to audio data of 11.6 msec.
Of the tracks accommodating data on the disc, the one desired for reproduction is accessed by the user selecting the appropriate track number through music selection procedures. Reproducing apparatuses usually have two keys for music selection: one for selecting the immediately following piece of music (UP key), the other for selecting the preceding piece of music (DOWN key). These keys are used to increment or decrement the track number, one at a time, until the number of the track storing the desired piece of music is reached.
In selecting a piece of music, however, the user often finds it troublesome to press the relevant key repeatedly, especially when the desired data track has a number that is considerably higher or lower than the currently selected track number. For example, if it is desired to select the 20th piece of music on the disc starting from track 0, it is necessary to press the UP key as many as 20 times. To play back the data track so selected further requires pressing a key that finalizes and enters the selection, which makes the manual operation even more tiresome.
Some reproducing apparatuses have numeric keys from 1 to about 25 so that the 20th piece of music, for example, may be selected by simply pressing the key "25." One disadvantage of this arrangement is an extensive space required over the control panel to accommodate the many numeric keys. The requirement runs counter to the recent trend of apparatuses getting smaller in size. In that sense, the many-key approach is not quite appropriate to all reproducing apparatuses. Even with a large number of numeric keys provided, the manual operation still remains troublesome if the keys fail to cover all track numbers of the disc. For example, if a disc contains 255 pieces of music and the numeric keys ranges from 1 to 25, any of the 26th through the 255th piece of music cannot be selected directly by a single numeric key operation; to select any of the pieces of music identified by the track numbers 26 and higher still requires operating the selection-related keys a number of times.
Some reproducing apparatuses may have an optional function permitting the entry of a character string representing the name of a piece of music or of a disc. In addition, the apparatus may incorporate a clock capability for displaying the time of day. A further optional function is one which allows the user to program desired pieces of music for playback in a desired sequence. Other optional functions include one that permits division of a data track in a desired position thereof (in what is called divide mode), and another allowing the track number to be moved up or down (in what is called move mode). The trouble is that executing any of these functions involves complicated manual key operations by the user.
That is, the user is required to press the relevant keys repeatedly when, illustratively, selecting the character string to be entered and then finalizing the selection. The same applies to setting the time of day with the clock function. More key operations are needed if it is necessary to carry out such steps as programming desired pieces of music to be played back in a desired order, setting the dividing position in divide mode, and selecting a different piece of music by moving up or down the track number in move mode.